1. Field of the Invention
A blood extraction device is known from U.S. Pat. No. 3,931,815 having a cylindrial extraction tube, a piston movable in an air-tight manner within said tube, a closure cap carrying a projection at the front end of the tube and a tubular guide sleeve which can be pushed onto the extraction tube. The guide sleeve carries at its front end a double-ended cannula having front and rear ends provided with respective cutting edges.
A closure plug puncturable by the cannula is arranged in the projection and the plug is made of a material which is self-sealing on removal of the cannula. The front end of the cannula which projects from the guide sleeve is provided for insertion into a vein whereas the rear end of the cannula is sealingly covered by a thin hose and projects sufficiently far into the guide sleeve that, on pushing the guide sleeve onto the extraction tube, the rear end of the cannula first of all punctures a rear end of the hose and then punctures the closure plug.
Axial guide means are provided between the guide sleeve and the extraction tube and are operative as the rear cutting edge of the cannula penetrates the closed rear end of the hose and then over at least a part of the movement of the rear cutting edge of the cannular through the material of the closure plug. In this arrangement the axial guide means takes the form of an axial tongue and groove guide provided between the extraction tube and the guide sleeve. The function of this axial guide means is to prevent relative rotation between the extraction tube and the guide sleeve when the actuating rod for the piston is screwed onto the piston. If the guide sleeve is pushed over the extraction tube the rear cutting edge of the cannula first of all cuts through the base of the rubber hose surrounding the rear end of the cannula and then through the closure plug at the front end of the projection on the closure cap of the extraction tube. Following this movement an annular rib provided on the inner wall of the guide sleeve snaps into a peripheral groove of the extraction tube so that further relative displacement between the guide sleeve and the extraction tube is avoided to a certain degree. This snap connection does not however adequately ensure that the required relative axial position between the guide sleeve and the extraction tube is retained during subsequent actuation of the piston arranged in the extraction tube.
It is also known (from German patent application No. P 18 12 742) to screw the guide sleeve onto an external thread provided on the projection of the extraction tube. This arrangement has, however, the disadvantage that the rear cutting edge of the cannula rotates as it passes through the base of the rubber hose and the closure plug. This can cause the rubber hose and the plug to wind up as they are penetrated which leads to a deterioration of the self-sealing characteristics of the penetrated parts on removal of the end of the cannula.
The principal object underlying the present invention is to provide a blood extraction device in which the guide sleeve can be easily slid onto the projection without disadvantageously affecting the self-sealing action of the punctured parts on removal of the cannula, and in which the axial position of the guide sleeve relative to the projection can be secured after it has been pushed onto the projection in such a way that a reliable connection is ensured between these components, even when strong axial forces act on the extraction tube.